JPH0375940B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an optical disk that can perform heat mode recording using, for example, a laser beam [Technical background of the invention and its problems] Recording formats are classified into three types shown in FIGS. 8 to 10. The type shown in FIG. 8 is one in which a laser beam is spot-irradiated onto a thin film 2 of a low-melting point material formed on a substrate 1 to melt and evaporate a local area, thereby recording a minute hole 3. In the type shown in FIG. 9, a multilayer thin film 5 consisting of two or more layers is formed on a substrate 4, and when a laser beam is spot-irradiated, bubbles are generated from the base layer 6 whose temperature has increased, and the upper thin film 5 is heated. This type is recorded as a bulge 8. In addition, the type shown in FIG. 10 forms a thin film 10 whose structure changes with temperature changes on a substrate 9, and changes local areas 11 of the thin film 10 into structures with different reflectances by spot irradiation with a laser beam. This is the type that is recorded. Since all of these types of recording parts 3, 8, and 11 have different characteristics of light transmission or reflection compared to non-recorded parts, a laser beam is used to
Recorded information is read by detecting the presence or absence of 8 and 11. However, among these types of recording forms, the types shown in FIGS. 8 and 9 irreversibly change the recording sections 3 and 8, and although recording is possible, erasing is not possible. Also, the 10th
The type shown in the figure enables recording and erasing by using a material whose optical properties change reversibly thermally as the recording film material. One example is a magneto-optical recording film.

On the other hand, it is well known that semiconductors such as Se, Ge, Te, and InSb can take two states: a stable crystalline phase and an amorphous phase, and the complex refractive index N = n-ik in each state. The difference is that J.STOUKE is J.
of.Non-Crystalline Solid vol 4 1 1970. The idea of creating an optical memory by reversibly changing the two states of this semiconductor, crystalline and amorphous, through laser beam heat treatment is SR.
Metsllurgical by OVSHINSKY et al.
Transactions vol 2 641 1971. However, thin films of these semiconductor materials are chemically unstable and have poor durability, so they have not been put into practical use. That is, Se, Ge, Te, InSb
Semiconductors such as these have the property of becoming amorphous when heated to a molten state and then cooled quickly, and become crystalline when heated to a lower temperature and slowly cooled.
The amorphous and crystalline phases are n′−ik′ and n
Although they exist stably with different optical properties characterized by the complex refractive index of -ik, these semiconductors have poor chemical stability when made into thin films and gradually corrode and deteriorate in the atmosphere, so they are not suitable for memory applications. It was not practical as a recording film for optical discs.

Subsequently, attempts have been made to make these semiconductors more durable by making them into compounds or sandwiching them between durable protective films, but these conventional techniques had the following drawbacks.

Known example 1 Non-erasable optical disk using phase change due to heating of a low oxide film of Te {Japanese Patent Publication No. 54-3725,
National Technical Report vol 28 1016 1982}
...In this example, TeOx, a low oxide of Te (0<x<
Although the thin film 2) is described as a recording film that undergoes a phase change, there is no mention of reversible changes in optical properties.

Known example 2 Erasable optical disk by reversible phase change of TeOx (x=1.1) thin film {Japan Society for the Promotion of Science Thin Film No.
131 Committee 116th Research Meeting Materials 1983}...In this example, Te with Ge and Sn added as trace impurities and TeO ₂ are simultaneously evaporated as decomposition products.
A thin film _of TeO _1,1 is deposited. As described above, a film that includes a decomposition process of TeO ₂ , which is unstable at high temperatures during the film formation process, has the disadvantage that it is difficult to control the quality.
In addition, TeO _1.1 is _specified by the above National Technical
As stated in Report vol 28 1016 1982, the reflectance of the film before recording is as low as about 15%;
Also, the change in reflectance due to recording is as small as about 12%, so optical disks made of this film have the disadvantage that it is difficult to perform focusing and tracking operations for the optical pickup for signal detection, and the readout signal is also small.

Publicly known example 3 Recordable/erasable optical disks (AEBell, etc.)
Appl.Phys.Lett vol 38 920 1981……In this example,
A thin film of pure Te, which has a large thermally reversible change in optical constant, was sandwiched between SiO ₂ films to protect its corrosion resistance and prevent Te from evaporating during heating.
It has a layered structure. This structure had the disadvantage that the thickness of each film had to be controlled correctly, making the film formation process complicated.

[Object of the invention] This invention was made in view of the above circumstances,
The purpose of this is to be able to record and erase data over a long period of time with excellent durability, and to obtain the interference effect of multiple reflections of light, resulting in a large amount of change in reflectance. To provide an optical disc which can obtain a reproduced signal of a nearly ideal size during reading, is simple to manufacture, has uniform quality, is inexpensive, safe and harmless.

[Summary of the invention]

In order to achieve the above object, the present invention provides a thin film on a substrate, irradiates the thin film with a light beam having information to be recorded, thereby locally causing a change in the optical characteristics of the thin film, and In an optical disk that can record and erase information using
It consists of a mixed film in which a semiconductor whose main component is Ge, Te or InSb is mixed in a chemically stable dielectric material at a volume ratio of 40% to 60%, and the mixed film and the substrate are A three-layer structure is formed with a semi-transparent film mainly composed of metal formed between them and a metal reflective film formed on the opposite side of the mixed film to the above-mentioned semi-transparent film. The three-layer structure has a thickness that causes multiple reflection interference upon light irradiation.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 shows the structure of an optical disc 20 of the present invention. This optical disk 20 includes a substrate (substrate) 21 made of glass, a recording film (thin film) 22 formed on this substrate 21, a metal film 27 having a high reflectance formed on this recording film 22, and the like. The protective film 23 is formed on the metal film 27 and protects the surface from scratches, making it a multilayer structure. As shown in FIG. 2, the recording film 22 is made of fine particle semiconductor (complex) whose optical constants change reversibly depending on the method of imparting thermal energy by the laser beam L, that is, exhibits two different stable optical states. Refractive index n-ik)24...
...is chemically a dielectric material (refractive index) that is particularly stable at high temperatures.
n ₀ ) 25, it is composed of a single mixed film that is dispersed and mixed by a volume ratio of 40% or more, and the effective optical thickness is less than 1/2 of the wavelength of the laser beam L. There is. Note that 26 is an objective lens for condensing the laser beam L onto the recording film 22.

In the recording film 22 configured in this way, the durability of the film is improved by reducing the volume content q of the semiconductor 24 in it, but the reflection amplitude at both interfaces decreases, and as a result, the synthesis Reflectance R decreases. As an example, FIG. 3 shows the change in reflectance over time when a sufficiently thick (1 μm or more) recording film 22 made of InSb and PbO is exposed to a high temperature and high humidity accelerated durability test atmosphere. As a result, it can be seen that forming the recording film 22 with a volume content q between 0.4 and 0.8 is a condition for obtaining a film that has both excellent durability and sufficient reflectance. . Another effect obtained by using such a mixed film is that when the volume content q is reduced, the absorption coefficient of the recording film 22 decreases from the value of the semiconductor 24 used, so that both boundaries of the film are reduced. This increases the interference effect of light reflected by the This effect is
This can be clearly seen from Figure 4, which shows the film thickness dependence of the reflectance of a mixed film made of InSb and PbO at a wavelength of 0.83 μm. This result shows that when a semiconductor with a large absorption coefficient is used as a mixed film with a dielectric material, it can function satisfactorily as a light interference film.

Therefore, with the configuration described above, when the semiconductor 24 in the recording film 22 undergoes a phase change due to laser beam irradiation, a sufficiently large combined reflection due to the interference effect occurs even if the volume content q is not 100%. The amount of change in the rate R can be obtained. As an example, the substrate 2
1. First, InSb and PbO with a volume content q of 60%
An optical disk 20 having a two-layer film structure is manufactured by forming a recording film 22 made of a mixed film of 1 and 2 and then depositing a Cu film as a metal film 27 to a thickness of 0.05 μm or more. When recording is performed on this optical disk 20 with a laser beam, the wavelength due to the phase change of the recording film 22 is
The film thickness dependence of the amount of change in reflectance for a readout laser beam of 0.83 μm is shown by a solid line in FIG. In the figure, + in the reflectance change amount indicates that the light becomes brighter, and - indicates that the reflectance becomes darker. The thickness of the recording film 22 can be determined from the figure.
It can be seen that the optical disc 20 manufactured to have a thickness of 0.055 μm is exposed to a change in reflectance of 50% or more (24%→77%) when recorded compared to when not recorded. In addition, the fifth
The curve shown by the dotted line in the figure shows the case where the volume content q is 1, that is, the recording film is formed only with InSb.
From the comparison of both curves, it is found that the optical disc 20 having the two-layer recording film of the present invention has a lower content of InSb and PbO.
It can be seen that even though it is as low as 60%, by using a laminated film, due to the interference effect, a large change in reflectance, that is, a reproduction signal level of recorded information, comparable to that of a 100% InSb film can be obtained.

According to such a configuration, the recording film 22 is made by dispersing the chemically unstable and poor durability semiconductor 24 as fine particles in the chemically stable dielectric material 25 that enables the phase change. Since the structure is such that the film is formed simultaneously by sputtering, the fine particles of the semiconductor 24 dispersed in the recording film 22 can easily transition to either the crystalline phase or the amorphous phase, and the recording The durability, which is important for the membrane 22, can also be significantly improved. In addition, the metal film 2
7 also has a structure in which the film is formed by sputtering, so it can be easily produced.

Furthermore, when the recording film 22 is locally irradiated with the laser beam L for a short period of time τ, the fine particles of semiconductor 24 contained therein are irradiated with the laser beam L.
is heated to a temperature θ proportional to the power of When the irradiation ends, the temperature of the semiconductor 24, which has reached a high temperature, decreases at a cooling rate of C=θ/2τ due to the flow of heat to the surrounding dielectric 25. Therefore, the semiconductors 24 in the irradiation section are cooled quickly when heated for a short time with a strong laser beam L, and slowly when heated for a long time with a weak laser beam L. That is, by selecting the method of applying the laser beam L, the semiconductor 24 included in the irradiated portion of the recording film 22 can be brought into a desired state of either an amorphous phase or a crystalline phase with different complex refractive indexes. I can do it. As a result, it is possible to convert the irradiated portion of the recording film 22 into a reflectance R determined by its complex refractive index, in other words, it is possible to record or erase.

Furthermore, by setting the effective optical thickness of the recording film 22 to 1/2 of the wavelength of the laser beam L (a thickness thinner than that at which the first reflectance minimum occurs), the recording film 22
has a relatively high reflectance both during recording and erasing, that is, both after erasing and after recording.
Not only information signals but also focusing signals and tracking signals can be made large.

That is, for example, the fine particle semiconductor 24...
InSb is used for the dielectric material 25, PbO is used for the dielectric material 25, and the entire recording film 2
InSb and PbO are sputtered simultaneously so that the volumetric filling rate of InSb in the substrate 21 is 60%.
The wavelength of the laser diode light in the recording part (amorphous phase) and erasing part (crystalline phase) of the recording film 22 deposited on
Reflectance R and reflectance change ΔR for 0.83μm
The film thickness dependence of is as shown in FIG. 5, and even if the recording film 22 has the same composition, the reflectance R and the amount of change in reflectance ΔR during recording and erasing will vary depending on the film thickness.
varies greatly due to the interference effect of reflected light on both surfaces of the recording film 22. Therefore, in this example, by setting the thickness of the recording film 22 to 0.05 μm, the reflectance of both the unrecorded area, that is, the erased area, and the recorded area can be increased, and the amount of change in reflectance can also be increased. This makes it possible to obtain a large read signal and facilitate the focusing and tracking servo operations of the signal detection optical pickup. Note that in this example, the recording film 22 is
InSb as the semiconductor 24, and as the dielectric 25
Although PbO was used, Ge as the semiconductor 24 also includes B ₂ O ₃ , Sb ₂ O ₃ , PbO, SiO ₂ ,
Oxides such as Ta ₂ O ₅ and BiF ₃ , LiF, PbF ₂ ,
Fluorides such as MgF ₂ , BaF ₂ , CaF ₂ , semiconductors 24...
...Te and InSb include B ₂ O ₃ , Sb ₂ O ₃ ,
A dielectric material 25 containing as a main component one or more of oxides such as PbO and fluorides such as BiF ₃ , LiF, and PbF ₂ is selected. In addition, although the volume filling rate of InSb in the entire recording film 22 was set to 60%, if the volume filling rate of the fine particles of the semiconductor 24 is small, the change in reflectance necessary for the recording film 22 will be small.
It has been confirmed through experiments that a value of 40 to 80 is suitable since a larger value reduces the durability required for an optical disk for memory.

Furthermore, because we have selected a combination of stable materials that do not decompose during the film formation process, it is easy to form a mixed film by simultaneously forming films, and since each layer is formed by sputtering, manufacturing is simple. and
Optical memory disks of uniform quality can be provided at low cost.

Further, in the recording film 22 having the above structure, even if it is damaged during handling as a disk or even if it is discarded, the semiconductor powder is exposed and will not scatter, making it safe and harmless.

In addition, in the above embodiment, the recording film and the metal film are
Although the layered film structure has been described, the present invention is not limited to this, and for example, as shown in FIG. It's okay. For example, the metal film 27 is a Cu film of 0.05 μm or more, the translucent metal film 28 is a Cu film of 0.01 μm, and the volume filling factor q is 60.
Recording film 2 consisting of a mixed film of InSb and PbO as %
FIG. 7 shows examples of characteristics obtained with optical disks for memory with different thicknesses. That is, with this structure, due to the interference effect of multiple reflections of light, the recording film 22
It has been shown that when the thickness of the film is set to 0.07 μm, the amount of change in reflectance due to recording reaches more than 80%. Such a change in reflectance provides a reproduced signal of a near-ideal magnitude, as if it corresponds to the presence or absence of a highly reflective point, when reading recorded information with a laser beam.

〔Effect of the invention〕

As detailed above, according to the present invention, a thin film is provided on a substrate, and by irradiating this thin film with a light beam having information to be recorded, a local change in optical characteristics is caused in the thin film. In an optical disk on which information can be recorded and erased using Ge,
It consists of a mixed film formed by mixing a semiconductor whose main component is either Te or InSb in a chemically stable dielectric material at a volume ratio of 40% to 80%, and between this mixed film and the substrate. A three-layer structure is formed by a semitransparent film mainly made of metal formed on the surface of the film, and a metal reflective film formed on the opposite side of the mixed film to the semitransparent film. The three-layer structure has a thickness that causes the interference effect of multiple reflections when irradiated, so it has excellent durability and can be recorded and erased over a long period of time. The change in reflectance is large, and when reading recorded information, it is possible to obtain a reproduced signal with a size close to the ideal.Furthermore, it is easy to manufacture, has uniform quality, is inexpensive, and is safe. We can provide optical discs that are harmless.

[Brief explanation of drawings]

Figures 1 to 5 show an embodiment of the present invention. Figure 1 is a cross-sectional view, Figure 2 is an enlarged cross-sectional view, and Figure 3 shows the relationship between the reflectance of the recording film and the exposure time. FIG. 4 is a diagram showing the relationship between the amount of reflection and film thickness of the recording film, FIG. 5 is a diagram showing the relationship between the amount of change in reflectance of the recording film and film thickness, and FIG. FIG. 7 is a cross-sectional view for explaining the configuration of the embodiment, and FIG. 7 is a diagram showing the relationship between the amount of change in reflectance of the recording film and the film thickness in FIG. FIG. 2 is a sectional view showing a conventional example. 21...Base (substrate), 22...Thin film (recording film), 24...Semiconductor, 25...Dielectric, 27...
...Metal film, 28...Semi-transparent metal film.

Claims (1)

[Claims] 1 A thin film is provided on a substrate, and by irradiating this thin film with a light beam containing information to be recorded, a local change in optical properties is caused in the thin film, thereby making it possible to record and erase information. In an optical disk, the thin film has optical constants that change due to the application of thermal energy by a light beam, and a semiconductor containing Ge, Te, or InSb as a main component in a chemically stable dielectric material with 40% ~80
% of the mixed film, and a semitransparent film mainly composed of metal formed between the mixed film and the substrate, and a side opposite to the semitransparent film with respect to the mixed film. 1. An optical disk having a three-layer structure including a metal reflective film formed on the semi-transparent film, and the three-layer structure having a thickness that causes interference effects of multiple reflections when light is irradiated from the semi-transparent film side.